DETROIT — Cory Booker’s campaign believes he finally had his moment in the Democratic presidential debate Wednesday night. Can he build on it now after months of struggling for traction?

Booker, the New Jersey senator, seized attention in clashes with front-runner Joe Biden, delivering his criticism with a mix of upbeat attitude and fight, emerging as a standout voice — at least for one night.

Even his sharpest dig came with a dose of humor.

“There’s a saying in my community: You’re dipping into the Kool-Aid and you don’t even know the flavor,” he told the former vice president, a line that has been endlessly replayed on cable news.

Booker sharply challenged Biden on criminal-justice reform and deportations during the Obama administration while keeping his signature smile during an event long on nasty and short on vision. And as his colleagues sniped at one another in desperate attempts to advance in the polls, Booker reminded the party of the need to focus on the prize.

“The person that’s enjoying this debate most right now is Donald Trump, as we pit Democrats against each other,” Booker said at one point.

A wide swath of analysts noticed, and declared Booker one of the few winners.

“This was his breakout moment,” said Brigid Harrison, a professor of political science at Montclair State University. “Where we are in the primary process, it’s clear the field will winnow, and this moment was necessary for Sen. Booker to move forward into the next round.”

Harrison said she thought Booker, often associated with a gentler style, was strong in his sparring with Biden.

“People saw last night just how effective a communicator he can be and how relevant his ideas are,” said Matt Klapper, the senior adviser to Booker’s campaign. He noted that Booker has received positive responses before, but “this just happened to be a really, really big spotlight.”

The moment came as Booker prepares to embark on a tour of swing states, including, Philadelphia next week, and Milwaukee on Aug. 11.

He capped his Detroit visit with an energetic rally at a downtown music venue Thursday evening, in which he preached a message of love and unity.

“We fight together or we will lose," Booker said, using references to the Bible and Martin Luther King Jr. “Love says we need each other because we share a common destiny and a common call.”

Hours after the debate, the campaign unveiled an endorsement from Mayor Jim Bouley of Concord, N.H., capital of the second state to vote in next year’s primary season.

>> READ MORE: Cory Booker 2020: How he could win. And why he might not.

Yet other candidates have shone for an instant, without lasting impact. Julian Castro, for example, impressed many in the first set of debates in late June, but has hardly budged in the polls. California Sen. Kamala Harris was hailed as the big winner in June and got a polling boost; it has since dissipated.

With the debate field set to narrow before the next debate, in September, due to tougher qualifying criteria, Booker might have won a chance to inject himself more fully into the conversation.

“It put him in a position for voters to continue to give him a second look,” said Patrick Murray, head of the Monmouth University Polling Institute. “So it might not have a significant movement in the polls, but it kept him in the mix.”

It’s not enough to gain attention for a night, said Mark Mellman, a Democratic strategist based in Washington. Candidates have to hold it.

“Sometimes these debates are a bit of a sugar high,” Mellman said. “The reality is, to win, you have to follow that up every single day with great performances on the stump, with endorsements, with policy rollouts."

Booker has attracted 1 to 3 percent support and remained well behind the top tier of candidates, despite considerable strengths. Perhaps no Democratic candidate has had a greater gap between potential and results.

Booker has for years been a national name with a sterling resumé — Stanford, Oxford, Yale Law — and was the subject of a documentary, Street Fight, in 2005. He has achieved quasi-celebrity status, was a finalist to be Hillary Clinton’s running mate in 2016, and delivered a keynote speech at that year’s Democratic National Convention in Philadelphia.

>> READ MORE: How Cory Booker’s ‘failed’ football career shaped his political future

As a 50-year-old black senator with soaring speaking skills, Booker seemed to have a chance to take hold in the Democratic electorate.

But it hasn’t happened. Analysts and people close to Booker have struggled to put their fingers on why, though a number of theories have emerged.

Booker aides have insisted that the senator is approaching the race as a slow build until voting begins next year, and that voters are still getting to know him, unlike Biden, who began with widespread name recognition.

Some have suggested that Booker has suffered from familiarity. Major news outlets have covered his rise for years, so he isn’t a fresh face or novel story like Mayor Pete Buttigieg. Others believe Harris, another black senator who is nearly the same age, overshadowed Booker with her early rollout. Biden, with strong appeal among African American voters, has dominated a constituency that Booker is relying on as a key part of his coalition.

(Biden enjoyed support from 53% of black Democratic voters, according to a Quinnipiac University poll released Monday; Booker had 2% in that group.)

And some have questioned whether the sunny Booker could be cutting when many Democrats are looking for a visceral fighter. On Wednesday he showed a mix of both.

“His feistiness, that is exactly what many Democrats are hankering for,” Harrison said. “It’s a feistiness, a toughness, but not incivility.”

Booker had foreshadowed the moment, sharpening his tone in recent weeks, particularly when it came to Biden’s record on crime and race. The fight was teed up for the senator, who has made criminal-justice reform his top issue in the Senate, while Biden has faced sharp criticism over his role in a tough-on-crime bill from 1994 widely blamed for fueling mass incarceration.

>> READ MORE: Criminal justice bill a major marker for Cory Booker as 2020 announcement looms

“This is one of those instances where the house was set on fire and you claimed responsibility for those laws. And you can’t just now come out with a plan to put out that fire,” Booker said.

Biden hit back by noting the aggressive police practices in Newark, N.J., when Booker was mayor there and hired a police commissioner who had served Republican Rudy Giuliani’s law-and-order administration in New York. It was a glimpse of what likely awaits Booker if he does rise.

“There was nothing done for the entire eight years he was mayor," Biden said, "There was nothing done to deal with the Police Department that was corrupt.”

Even amid that exchange, Booker managed a dose of levity, jabbing, “If you want to compare records — and, frankly, I’m shocked that you do. ...” It drew laughter in the debate hall.

The attack on Biden’s criminal-justice record not only put Booker in the spotlight, it gave him an avenue to try to cut into the former vice president’s standing with black voters, who fondly remember his work alongside Barack Obama.

Booker made an explicit appeal to that key Democratic demographic, arguing that the party lost Michigan in 2016 because “everybody from Republicans to Russians were targeting the suppression of African American voters."

Moses Bell, a Booker supporter who chairs the Fairfield County Democrats in South Carolina, another early-voting state, called the debate his strongest moment.

“You know and I know that he hasn’t been able to get traction in South Carolina, but I think this will help him," Bell said. “What he said about black votes being suppressed. Nobody talks about that, and it is absolutely the truth.”

But Bell cautioned Booker shouldn’t go too far in criticizing Biden, especially if he’s hoping to win over more African American voters.

“He knows local communities," Bell said. "That’s what he has. That’s his gift. He understands people. His gift is not to attack. ... His heart is what gets us to a place of fairness and equity in this country. That’s his strength. Stick to your strength.”